1. Field of the Invention
The invention relates to a double walking beam furnace for the heat treatment of individual parts, for example sheet metal, comprising a transport apparatus for conveying the parts to be treated through the furnace, the transport apparatus having two groups of longitudinal beams which alternatively transport the parts in a stepwise manner. These longitudinal beams are alternatively arranged adjacent one another in spaced relationship, a sub-structure being provided beneath each longitudinal beam and supporting and moving together with this, the sub-structure effecting the vertical movement and the horizontal movement in the longitudinal direction of the furnace of the longitudinal beam and of the bottom part of the furnace which is usually arranged beneath and moved together with the beam. Between two respectively adjacent sub-structures, a water trough is arranged which extends approximately over the entire furnace or hearth length and is immovable with respect to the base assembly. Dip skirts arranged on the neighbouring sub-structures and movable together with these are immersed in the respective water trough in order to seal the furnace at its bottom in a gas-tight manner. The water troughs are made up of separate longitudinal channels for constructive reasons.
2. Description of the Related Art
In known double walking beam furnaces of this kind, the longitudinal channels of the water troughs are provided at their abutting end faces with outwardly projecting flanges which are bolted together with sealing strips arranged therebetween in order to achieve a secure and liquid-tight joint of the abutting longitudinal channels.
In view of the fact that the individual parts to be treated in the furnace must be supported on at least two longitudinal beams per beam group and sheet-like parts should, for reasons of support, not or only slightly project laterally over the displacable beams supporting the parts, a centre-to-centre spacing between the adjacent displacable beams of both beam groups which is as small as possible is desirable. In the double walking beam furnaces known up to now, it was not possible for reasons of the structurally limited minimum cross sectional dimensions of the water troughs and dip skirts as well as the supporting or sub-structures of the longitudinal beams located at approximately the same height to realize a centre-to-centre spacing of less than 400 mm so that the transport of thin sheeting resulted in significant problems on account of the existing danger of too great a lateral projection over the edge.